In some engines, an electronically controlled throttle is used for improved performance. In such systems, position of the throttle is controlled via closed loop feedback control. Typically, to provide redundancy multiple throttle position sensors are provided.
One method to provide two throttle position sensors uses sensors of different gradients, each linear over the entire operating range, another uses gradients of opposite sign. Still other methods use saturating sensors. These methods are described U.S. Pat. Nos. 5,136,880; 5,260,877; and 4,693,111, respectively.
The inventors herein have recognized some disadvantages of the above approaches. In particular, when a high resolution saturating sensor and a low resolution sensor are used together, there is a saturated region where the saturating sensor provides less information than the unsaturated region. Alternatively, when different gradients are used, each linear over the entire region, the analog to digital converters are over-specified and under-utilized to accommodate the low resolution sensor. Another disadvantage with prior approaches is that multiple tracks, interconnections between the tracks, and wiper arms may be required to provide multiple outputs having different characteristics.
An approach to solve the above prior art disadvantages would be to have a sensor with two output signals. The first output signal would be linear over the entire operating region. The second output signal would have two segments, each of said segments having a different resistivity. The second output would therefor have two segments, each with a different gradient, and having a point of non-linearity.
Having a sensor with two operating regions gives that opportunity to obtain high resolution at low throttle angles, and thereby have better airflow control, as well as obtain information throughout the operating range without over-specifying and under-utilizing A/D converters.
However, the inventors herein have recognized a disadvantage with such a sensor. In particular, the output having two segments may have variation due to manufacturing. As such, the point of non-linearity may have increased error. Such error may cause degraded control.